# Interdomain communication

# Invoke Javascript from Python

window.evaluate_js(code, callback=None) allows you to execute arbitrary Javascript code with a last value returned synchronously. If callback function is supplied, then promises are resolved and the callback function is called with the result as a parameter. Javascript types are converted to Python types, eg. JS objects to dicts, arrays to lists, undefined to None. Note that due implementation limitations the string 'null' will be evaluated to None. You must escape \n and \r among other escape sequences if they present in Javascript code. Otherwise they get parsed by Python. r'strings' is a recommended way to load Javascript. For GTK WebKit2 versions older than 2.22, there is a limit of about ~900 characters for a value returned by evaluate_js.

# Invoke Python from Javascript

Invoking Python functions from Javascript can be done with two different approaches.

  • by exposing an instance of a Python class to the js_api of create_window. All the callable methods of the class will be exposed to the JS domain as pywebview.api.method_name with correct parameter signatures. Method name must not start with an underscore. See an example.
  • by passing your function(s) to window object's expose(func). This will expose a function or functions to the JS domain as pywebview.api.func_name. Unlike JS API, expose allows to expose functions also at the runtime. If there is a name clash between JS API and functions exposed this way, the latter takes precedence. See an example.

Exposed function returns a promise that is resolved to its result value. Exceptions are rejected and encapsulated inside a Javascript Error object. Stacktrace is available via error.stack. Functions are executed in separate threads and are not thread-safe.

window.pywebview.api is not guaranteed to be available on window.onload. Subscribe to window.pywebviewready instead to make sure that window.pywebview.api is ready. Example.